Life jackets and rafts which are held in readiness aboard vessels and aircraft are usually in a tightly packed condition until inflated for use. The inflation is preferably carried out automatically even though it may also be carried out manually.
Before being put into use a light source arranged on life jackets or rafts should be switched on by supplying power from a long-storage-life battery. The light source may be switched on manually but, of course, it is desirable that it is switched on automatically when the life jacket or raft is exposed to water.
In order to comply with international demands the light source of a life jacket or a raft should be capable of flashing the light source between 50 and 70 times per minute for a period of at least 8 hours. The typical switching sequence involves that the light source is switched on in period of 0.3 s. This on-period is followed by a period of 0.7 s where the light source is switched off. During the full 8 hours the lamp should be capable of delivery a light intensity of 0.75 candela.
It is a disadvantage of known systems that the light intensity from the lamp decreases over time. This decrease in light intensity is primarily caused by a decreasing battery voltage which in known devices may decrease up to 30% over 8 hours. In case of for example a 3 V lithium battery, the battery voltage may decrease down to around 2 V over a period of 8 hours. Initially, the battery voltage is sufficient to drive the light source so that it generates a light intensity that exceeds international demands (0.75 candela) with a relative large margin. However, due to the decreasing battery voltage over time, the generated light intensity decreases accordingly whereby the safety margin to the required 0.75 candela is reduced as well.
Moreover, scattering of light over approximately 180 degrees, which correspond to a hemisphere, has proven difficult without implemented a relatively high lens structure. However, high lens structures are disadvantageous in maritime applications because for example clothes may be caught in such high lens structures with the risk of damaging the lens structures.
It may be seen as an object of embodiments of the present invention to provide a modular maritime light source suitable for being mounted or integrated in life jackets and/or rafts.
It may be seen as a further object of embodiments of the present invention to provide a maritime light source offering improved light scattering properties using a flat lens structure.
It may be seen as a still further object of embodiments of the present invention to provide a maritime light source offering a plurality of selectable functionalities, such as manual or automatic water activation, internal or external water activation etc.
It may be seen as a still further object of embodiments of the present invention to provide a maritime light source having a low component count, suitable for mass production and flexible design features.